1. Field of the Invention
The present invention relates to a golf ball, and more particularly, to the golf ball having an improved aerodynamic symmetrical property which can be accomplished by arranging dimples of different surface configurations on the surface thereof.
2. Description of the Related Arts
Normally 280 to 540 dimples are formed on the surface of the golf ball. The function of dimples is to reduce pressure resistance to the golf ball during flight and improve the dynamic lift thereof. More specifically, in order to lift a golf ball high in the air, the separation point between the air and the upper surface of the ball is required to be toward the back of the ball as possible compared with the separation point between the air and the lower surface thereof so as to make air pressure existing above the ball smaller than that which exist below the ball. In order to accelerate the separation of air existing above it from the upper surface thereof, it is necessary to make the air current along the periphery of the ball turbulent. In this sense, a dimple which makes the air current around the golf ball turbulent, is aerodynamically superior.
Since the golf ball is molded by a pair of upper and lower semispherical molds having dimple patterns, dimples cannot be arranged on the parting line corresponding to the connecting face of the upper and lower molds. Therefore, one great circle path corresponding to the parting line which does not intersect any dimples is formed on the surface of the golf ball.
As the surface configuration of the dimple, circular, elliptic, polygonal or the like is adopted. The golf ball has dimples of the same surface configuration or various surface configurations formed on the surface thereof.
In view of the dimple effect, the surface of the golf ball may be divided into a spherical zone in the vicinity of a great circle path, not intersecting any dimples and other spherical zone with respect to the great circle path. According to conventional methods of arranging dimples of different surface configurations, both spherical zones have the same dimple arrangement, i.e., dimples which are uniformly arranged throughout the surface of the golf ball.
When dimples of different configurations are arranged on the surface of the golf ball uniformly in both spherical zones, the dimple effect in the spherical zone in the vicinity of the great circle path is differentiated from the other spherical zone due to the existence of the great circle path. Consequently, the following problem occurs in the aerodynamic symmetrical property of the golf ball.
It is preferable that the golf ball flies in the same trajectory each time it flies. That is, preferably, the trajectory height, flight time, and flight distance of the golf ball is the same, respectively, regardless of whether or not its rotational axis in its backspin coincides with the great circle path. But actually, dimple effect varies according to a rotational axis, namely, whether or not a circumference which rotates fastest in its backspin coincides with the great circle path.
More specifically, in line hitting, i.e., when the golf ball rotates in its backspin such that a circumference which rotates fastest in its backspin coincides with the great circle path, the dimple effect of making air current around the golf ball turbulent is smaller than the dimple effect obtained in face hitting, i.e., when the golf ball rotates in its backspin such that a circumference which rotates fastest in its backspin does not coincide with the great circle path. That is, the trajectory height of the golf ball is lower and consequently the flight time thereof in line hitting is shorter than those in face hitting.
If the golf ball has a different flight performance according to a rotational axis, i.e., if the golf ball has an unfavorable aerodynamic property, a player's ability cannot be displayed.
In order to solve the above-described problem, methods for manufacturing golf balls having no great circles are proposed, for example, in Japanese Patent Laid-Open Publication 64-8983 and Japanese Patent Laid-Open Publication No. 62-47379. However, due to various problems, these methods are incapable of putting golf balls on the market. Such being the case, golf balls commercially available have at least one great circle path.